Role of carboxylate bridges in modulating nonheme diiron(II)/O2 reactivity
Role of carboxylate bridges in modulating nonheme diiron(II)/O2 reactivity
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DOI：
10.1021/ic034359a
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发表时间：
2003-11-17
影响因子：
4.6
通讯作者：
Que, L
中科院分区：
文献类型：
--
作者：
Costas, M;Cady, CW;Que, L
合成了一系列双核配体HPTP（N，N，N，N-四（2-吡啶甲基）-2-羟基-1，3-丙二胺）与一个或两个羧酸桥形成的二铁配合物，并对其结构进行了表征。已获得每个子集的一个成员的晶体结构，以揭示子集A的（μ-烷氧基）（μ-羧基）二铁（II）中心与一个五配位和一个六配位金属离子和子集B的配位饱和（μ-烷氧基）双（μ-羧基）二铁（II）中心。这些配合物与O-2在二阶过程中反应，形成特征为（mu-1，2-peroxo）diiron（III）配合物的加合物。停流动力学研究表明，氧合步骤是敏感的二铁（II）中心上的O-2结合位点的可用性，作为子集B反应更慢的数量级。O-2加合物的寿命也是不同的，并且可以通过添加氧供体配体来调节。单羧酸络合物的O-2加合物通过必须通过停流方法监测的快速二阶过程衰减，但在CH 2Cl 2/DMSO（9：1 v/v）中变得稳定，并通过慢得多的一阶过程分解。二羧酸络合物的O-2加合物在纯CH 2Cl 2中甚至更稳定，并通过一级过程衰变。加合物稳定性的这些差异反映在观察结果中，即只有单羧酸盐络合物的O-2加合物可以氧化底物，并且只有那些可以与二铁中心结合的底物。因此，二羧酸盐络合物的O-2加合物的更大稳定性可以通过形成（μ-烷氧基）（μ-1，2-过氧基）二铁（III）络合物来合理化，其中二铁（II）络合物中的羧酸盐桥变成O-2加合物中的末端配体，占据二铁中心上的剩余配位位点，并防止潜在底物的结合。非血红素二铁酶的氧化机制的影响进行了讨论。
A series of diiron(II) complexes of the dinucleating ligand HPTP (N,N,N,N-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-diaminopropane) with one or two supporting carboxylate bridges has been synthesized and characterized. The crystal structure of one member of each subset has been obtained to reveal for subset A a (mu-alkoxo)(mu-carboxylato)diiron(II) center with one five- and one six-coordinate metal ion and for subset B a coordinatively saturated (mu-alkoxo)bis(mu-carboxylato)diiron(II) center. These complexes react with O-2 in second-order processes to form adducts characterized as (mu-1,2-peroxo)diiron(III) complexes. Stopped-flow kinetic studies show that the oxygenation step is sensitive to the availability of an O-2 binding site on the diiron(II) center, as subset B reacts more slowly by an order of magnitude. The lifetimes of the O-2 adducts are also distinct and can be modulated by the addition of oxygen donor ligands. The O-2 adduct of a monocarboxylate complex decays by a fast second-order process that must be monitored by stopped-flow methods, but becomes stabilized in CH2Cl2/DMSO (9:1 v/v) and decomposes by a much slower first-order process. The O-2 adduct of a dicarboxylate complex is even more stable in pure CH2Cl2 and decays by a first-order process. These differences in adduct stability are reflected in the observation that only the O-2 adducts of monocarboxylate complexes can oxidize substrates, and only those substrates that can bind to the diiron center. Thus, the much greater stability of the O-2 adducts of dicarboxylate complexes can be rationalized by the formation of a (mu-alkoxo)(mu-1,2-peroxo)diiron(III) complex wherein the carboxylate bridges in the diiron(II) complex become terminal ligands in the O-2 adduct, occupy the remaining coordination sites on the diiron center, and prevent binding of potential substrates. Implications for the oxidation mechanisms of nonheme diiron enzymes are discussed.